DNA microarray chips are well known in the prior art. Such microarrays are typically formed either by on-chip photolithographic synthesis of oligonucleotides1 or by on-chip spotting of synthesized oligonucleotides.2 Both approaches have significant limitations. The photolithographic synthesis method is expensive, limited to 50-mer oligonucleotide synthesis, and cannot be used for cDNA. The spotting method uses expensive robots and pins, and wastes the oligonucleotide samples unless many microarray slides are prepared during one spotting procedure. In both cases, each microarray slide created can be used with only one sample. Therefore, multiple samples typically require the use of multiple microarray slides. Moreover, microarray slides usually require large volumes of sample (e.g. 200 μL).
In some cases the spotting method has been performed on chips containing microfluidic channels.3, 4, 5, 6, 7 While spotting oligonucleotides into a microfluidic channel may reduce the required sample volume, the density of the resultant microarray is limited by the space required on the chip required to accommodate complicated liquid handling interfaces, such as microtubes, micropumps electrical contacts and the like. Heretofore high density microarrays have not been successfully achieved using microfluidic techniques. For example, some groups have used a stencil approach to create parallel, linear microfluidic channels on separate chips.8, 9, 10, 11 The microfluidic channels are then used to generate microarrays at intersecting points between the linear channel patterns. However, this approach has thus far not been employed to generate high density arrays (i.e. greater than about 16×16 channels).12 This is likely due to the difficulty in reliably flowing reagent fluid through large numbers of microchannels using conventional fluid delivery techniques, such as electrical current or pressure pumping. For example, it is technically difficult and cumbersome to couple miniature electrical connections or pump conduits to large numbers of microchannels without causing fluid leakage or other undesirable chip failures.
Apart from electric and pressure pumping, the use of centrifugal force is known in the prior art in some DNA hybridization applications using pre-spotted microarrays.13, 14, 15, 16, 17, 18, 19, 20, 21 For example, DNA hybridizations have been achieved on circular discs in which centrifugal force has been used to pump liquids through radial channels in which a microarray is spotted.22 However, in this example the liquid pumping method is used in the radial direction only and is used only once on the chip. Centrifugal pumping has thus far not been used to form an intersecting pattern of reagents on a microarray chip.
The need has therefore arisen for improved devices and methods for producing microarray devices using microfluidic techniques to enable the efficient testing of multi-probe, multi-sample reagent combinations.